I was trying to check the documentation for handleNewUDPFlow over at https://developer.apple.com/documentation/networkextension/neappproxyprovider/3192017-handlenewudpflow and... it says it's deprecated on everything. Retroactively.
I think the documentation pages have been borked a bit...
This may be an issue of timing in the documentation. I believe this is due to the updates made for NWEndpoint, and so this changed the method signature here. Can you open a bug report for this here, in case one is not already opened, and I can make sure it goes to the right place. Please post the Feedback ID here.
Matt Eaton - Networking
What changes were made to NWEndpoint?
I filed FB14076199